Solid state motor starers control the stopping and staring of electrical motors by gated semiconductor devices such as SCRs or other thyristors. A concern in solid state motor starers is the amount of heat generated by the semiconductor switching devices particularly when the motor is running between start-up and stopping operations. This problem becomes more acute as the enclosures for such control are made more compact and/or contain more equipment.
One method of minimizing the heat generated by solid state motor starter systems is to employ an electromagnetic by-pass contactor electrically connected in parallel with the semiconductor switching device(s) for each phase of the starter. The semiconductor switching device is commonly clamped between a pair of heat sinks which are in electrical circuit with the respective semiconductor switching device. Accordingly, the bypass contactor is commonly wired to the heat sinks by providing electrical connector lugs on the heat sinks. The size wire required for such applications is quite large and therefore the bending radius for the wire is similarly very large. Each phase, or pole, of a solid state motor starter requires a bypass contactor. Accordingly, the size and quantities of contactors required and the large wire bending area occupy considerable space within the enclosure. As stated above, it is a trend in present day motor starter design to reduce the overall size of the starter, hence the enclosure, which requires the individual components of the starter to be smaller in size and more closely arranged within the enclosure.